1. Field of the Invention
The present invention relates to a subscriber network system using the ATM (Asynchronous Transfer Mode) transmission mode.
2. Description of the Prior Art
A subscriber network system is thought of as a system capable of high-speed, broad-band communication, with fiber optic cables installed to subscriber homes. Today, a Passive Double Star (PDS) system is the most promising candidate for this subscriber network system because it is lowcost. However, many problems must be solved to realize a PDS system. One of them is a system control problem.
One of the documents which describe this system control is "ATM based Passive Double Star System offering B-ISDN, N-ISDN, and POTS", by Y. TAKIGAWA et. al., GLOBCOM '93, pp. 14-18 (December 1993). This document describes how to transmit signals in a PDS system using the ATM transmission technique.
However, the above document does not describe the technique for system control; it only describes physical layer OAM cells. Normally, these physical layer OAM cells are provided for detecting and indicating abnormal conditions, such as signal disruptions or duplications, or for sending error information to a connection termination point, but not for the system control operation. For example, in the conventional system, information on a subscriber unit installed at a subscriber home is not sent to the local switch, nor is control information sent from the local switch to a subscriber home.
Another method of controlling the system is to use a fixed area within a frame. This cannot be used in multimedia communication for the following reason. Multimedia communication requires the broad-band transmission mode which, in turn, requires the ATM transmission technique. However, in the ATM transmission technique, it is impossible to reserve a fixed area within a frame for use as the system control operation.
In view of the foregoing, the realization of a configuration for controlling the system has long been awaited.